“Once a merger has been accepted by both parties, the faction (AKA Faction A) sending the original request will merge into the receiving faction(AKA Faction B), dissolving Faction A.
Every asset owned by Faction A shall then be merged into Faction B, including unique datacards and members. However, when merging datacards, datacards only get merged if they match the production type of the group they are merging to. ”

So the result of a merger is ... one faction, one tech tree. I really wonder why you think it might be different.

You will. Ship factions will get access to the ship tree, vehicle factions the vehicle tree, etc. Govs might have access to more than one, I suppose it depends on whether govs get their own tree, or will be left to grab from others.